Cancer Stem Cells: Root of the Evil

Cancer stem cells (CSCs) have been one of the most attractive research areas over the last two decades due to their important roles in aggressive tumor behaviors. Although CSCs are usually a small subpopulation of tumors (less than 0.1%), these cells determine the fate of cancer patients because of their roles in poor prognoses. Accumulating evidence has shown that CSCs are the major responsible cell population in tumor development, growth, metastasis, and therapy resistance. The self-renewal and differentiation capacity of CSCs contribute to the initiation and maintenance of tumor growth. Several reports indicate that CSCs share numerous molecular characteristics with mesenchymal cells, so CSCs are accepted as leading players in metastasis. In addition, these cells possess a higher intrinsic resistance to chemotherapies and radiotherapies than bulk cancer cells. Therefore, therapeutic approaches in recent years have focused on effectively targeting CSCs. Here, we have reviewed the current literature on the resistant mechanisms of CSCs, their roles in metastasis, and the roles of non-coding RNAs in the regulation of aggressive CSC characteristics and novel therapy approaches against CSCs.